FIELD OF THE INVENTION
The invention relates to a device for supporting and electrically contacting brushes, with which an electrical loop contact can be established to slip-rings on a shaft of a current generator. During the operation of generators, an induction current coming from stationary units is transmitted to slip rings of a rotor shaft.
Such devices have been known for a long time and generally function reliably over long periods of times. A device of that type is known from German Utility Model G 94 00 080.8, in which brushes are movable between a working position and a standstill position. In the working position an electrical contact exists between the brushes and the slip-ring, although not in the standstill position. Safe electrical contact in the working position is achieved through the use of mobile parts of the device and a contact pressure.
However, devices of that type with fixed parts for supporting the brushes are also known. That requires a particularly stable construction of the device. In a known structural form, several pins are fixed to a supporting base. The supporting base is made of metal and the pins are made of an insulating material. The pins are disposed around the rotation axis of the shaft. At least one sleeve made of electrically conductive material is pushed over each pin, in order to establish electrical contacting with the brushes. The brushes themselves are held by a holder which can be inserted onto the sleeves or pulled out from them. Generally, exactly two sleeves are pushed over each pin which, due to the insulating effect of the pin and a spacer between the sleeves, helps current transmission to two different slip-rings, that have a different electrical potential during operation of the current generator or the electrical motor. The sleeves for current transmission to the same slip-ring are always components of a current distributor. Part of a current distributor is also formed by a partly ring-shaped current rail, with which the sleeves are short-circuited, and a current connection rail with holes for fixing and connecting an electrical connection line. The connections between the current rails and the connections between the partly ring-shaped current rail and the sleeves are ensured through the use of rivets or screws.
German Published, Non-Prosecuted Patent Application DE 40 09 851 A1 discloses a short-circuiting and brush-lifting mechanism for asynchronous motors with slip-ring rotors, which work wear-free to a large extent and are insensitive to impurities. With the help of a rotatable actuation ring having brush actuation guides, the brushes are only removed when the slip-rings have been short-circuited.
The above-described device is used with a great deal of reliability in continuous operation of electrical machines. It is, however, composed of up to 250 individual parts. Since the assembly generally takes place only at the site of the machine, a relatively high expenditure for storage and assembly of the components is unavoidable.
U.S. Pat. No. 1,582,712 relates to a brush holder for electric machines. Bolts which are disposed on an electrically conductive ring are directed, at equal spacings along the circumference of the ring, parallel to the ring axis. Electric brushes can be connected mechanically and electrically to the bolts. The ring is surrounded, at equal spacings over its circumference, by a number of magnetic elements. In each case two magnetic elements thus enclose a group of bolts. Electric current is fed, through a lead in each case, to each group of bolts. Electric current flowing through the electrically conductive ring from one group of bolts into the other group of bolts is damped as it passes through the group-separating magnetic element since the magnetic element produces a high impedance for that current. As a result of that division of the bolts into groups through the use of the magnetic elements, the current paths to the individual plug-in brushes are essentially identical, and thus the currents through the individual plug-in brushes are likewise essentially identical.
French Patent Application No. 1 537 426 concerns an annular plug-in brush holder for electric machines. That French Patent Application deals exclusively with a ring which connects and secures the plug-in brushes. The object of French Patent Application No. 1 537 426 is to provide increased operational reliability. That is achieved in such a way that the electrically conductive electric connection connecting the plug-in brushes is routed within an insulating ring which includes two mutually opposite ring parts that butt directly against one another. In each case an electric conductor is routed within one annular groove. The respective contact bolts of the plug-in brushes are connected to the electric conductors.